Shear Flow/Complex flow-induced polymer chain scission in entangled melts

In this study, shear flow and complex flow-induced polymer scission are analyzed to enhance depolymerization processes for upcycling. Chemical upcycling of commercial plastics is intended to produce intermediate molecules through depolymerization, often catalytically. However, catalytic reactions are hindered in polymeric systems by high viscosity and low transport to catalytic sites. An enhancement is to induce polymer scission either mechanically or thermally as a pre-process step or in parallel to catalytical upcycling. Polymer processing operations like extrusion are well known to degrade polymers, due to a combination of flow types (shear and extension). However, flow-induced scission is not well-understood since it is hard to distinguish nor is the quantitative impact of flow type. Here, we strive to decouple the impact of flow type and duration on overall chain scission. Particularly, we analyse shear-induced scission and complex (shear + extension) flow-induced scission with rotational rheometry and micro-compounders. We focus on entangled polymer melts and the impact of entanglement molecular weight. Optimal flow conditions (total strain, flow rate and the flowing time) are studied for hydrogentaed-PI. Nonlinear shear flows of varying type and duration are applied while complex flows of varying screw speed and duration are applied. The impact of shear flow on overall molecular weight is tracked in situ through SAOS and compared to ex situ detailed measurement of molecular weight distribution. Scaling of scission with work of flow, flow type and flow duration are considered.